src: fix to use replacement character

PR-URL: #43999
Fixes: #43962
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Mohammed Keyvanzadeh <mohammadkeyvanzade94@gmail.com>
Reviewed-By: Darshan Sen <raisinten@gmail.com>
Reviewed-By: LiviaMedeiros <livia@cirno.name>
Reviewed-By: Feng Yu <F3n67u@outlook.com>

src/node_i18n.cc

@@ -425,7 +425,11 @@ void ConverterObject::Create(const FunctionCallbackInfo<Value>& args) {
                         nullptr, nullptr, nullptr, &status);
   }
 
-  new ConverterObject(env, obj, conv, flags);
+  auto converter = new ConverterObject(env, obj, conv, flags);
+  size_t sublen = ucnv_getMinCharSize(conv);
+  std::string sub(sublen, '?');
+  converter->set_subst_chars(sub.c_str());
+
   args.GetReturnValue().Set(obj);
 }
 

test/parallel/test-whatwg-encoding-custom-textdecoder.js

@@ -199,3 +199,10 @@ if (common.hasIntl) {
   const str = decoder.decode(chunk);
   assert.strictEqual(str, 'foo\ufffd');
 }
+
+if (common.hasIntl) {
+  const decoder = new TextDecoder('Shift_JIS');
+  const chunk = new Uint8Array([-1]);
+  const str = decoder.decode(chunk);
+  assert.strictEqual(str, '\ufffd');
+}